Dworshak Dam Spillway and Outlet Hydraulic Design

Hydraulic design of spillway and outlets for 693-ft-high concrete-gravity dam utilizes model studies in developing final design. Tainter valves provide upstream control in the three outlet conduits. The valves seal through the action of an eccentric-trunnion mechanism, which moves the valve upstream against the seals. The outlet conduits enter the spillway chute at a point about midway between the spillway crest and stilling basin. Special training-wall arrangements are developed in the model to minimize spray and spillway flow disturbances resulting from the outlet portals in the spillway chute. The conduit intakes, under about 250 ft of head, required special study in the model because of a lack of back pressure and because of a horizontal and a vertical skew with respect to the upstream face of the dam. Facilities for study of spillway boundary layer development and other problems in the prototype are included in the design.